Arc printing of characters

ABSTRACT

There is disclosed a system for arc printing characters such as numbers or letters on a metallic film bearing substrate. Features of the invention include perpendicularly moving a character shaped electrode into contact with the metallic film bearing substrate, wiping the character shaped electrode to remove metallic particles adhering thereto, and providing a resilient backing member for supporting the film bearing substrate when the electrode is pressed thereagainst. In addition, details of the operating parameters for arc printing characters is disclosed.

United States Patent [191 Bolger, Jr.

[ Sept. 11, 1973 ARC'PRINTING OF CHARACTERS [75] Inventor: John G. Bolger, Jr., Orinda, Calif. [73] Assignee: Di gilux Corporation, Oakland, Calif. 221 Filed: Mar. 15, 1972 [21 Appl/No; 234,889

521 U.S.Cl 219/216, 346/74S [51] 1nt.Cl. 1105b 3/16 53 FieldotSearch ..2l9/2l6, 383, 384,

219/69 M, 69 V, 234; 346/74 SB, 74 S, 74 SC, 74 ES; 179/100.2 D; 355/12 [56] References Cited UNITED STATES PATENTS 2,785,280 3/1957 Eisler et al.... 219/69 V 3,419,886 (12/1968 Ortlieb....=. 7 346/74 SB 3,449,528 6/1969 Camras 179/1002 D 3,411,948 11/1968 Reis 346/74 SB Primary ExaminerC. L. Albritton AttorneyColton & Stone [57] ABSTRACT There is disclosed a system for are printing characters such as numbers or letters on a metallic film bearing substrate. Features of the invention include perpendicularly moving a character shaped electrode into contact with the metallic film bearing substrate, wiping the character shaped electrode to remove metallic particles adhering thereto, and providing a resilient backing member for supporting the film bearing substrate when the electrode is pressed thereagainst. In addition, details of the operating'parameters for arc printing characters is disclosed, v v

7 Claims, 2 Drawing Figures POWER 1 SUPPLY n I ARC PRINTING F CHAKACTERS BACKGROUND OF THE INVENTION Printing information on metallic film bearing substrates by arcing discrete areas of the film from the substrate is well known in the art. The typical are printing arrangement incorporates a stylus which is moved laterally across the substrate to are off the film in a desired fashion. Typical disclosures of this type are found in U.S. Pat. Nos. 2,836,479 and 3,074,066. Exemplary recordable media for conventional are printing techniques are found in U.S. Pat. Nos. 2,687,361; 2,808,345 and 2,833,677. The backing or substrate of these recordable media are typically opaque so that the information recorded thereon cannot be optically projected for reading. It has been suggested, however, in U.S. Pat. No. 3,256,524 to utilize an analogous technique for removing a metallic coating in a pattern from a transparent substrate in order to produce an optically projectible image. 7

All the prior art presently known to applicant involving are printing relates to the removal of small dots from the metallic coating or laterally moving the stylus across the coating to create a trace which'is indicative of some type information. It is not apparent that characters have been previously printed on metallic film bearing substrates without laterally moving a stylus along the substrate in the shape of the character to be encoded.

As will be more fully apparent hereinafter, this invention involves the printing of characters on a metallic film bearing substrate simply by pressing a character shaped electrode against the film in amanner analgous' to a typewriter key pressing against paper and passing electrical energy through the electrode. During the development of the invention, a number of problems arose which were not anticipated from the conventional arc printing techniques utilizing a stylus. For example, it was discovered that commercially available are printing paper did not work satisfactorily. Upon investigation, it was determined that the larger contact area of the character shaped electrodes necessitates a relatively high current to establish the current density necessary to remove the film. In order to support the printing current, the film must be substantially thicker than that required for'single point or stylus printing. Additionally, it was discovered that printing quality rapidly deteriorates after a few printing cycles with the same electrode. Another problem that arose relates to the voltage requirement for breaking down the surface oxide layer of the metallic film. In the case of a relatively small surface area stylus point, mechanical penetration of the surface oxide layer to establish good electrical contactwiththe metallic film thereunder is easily effected. In order to obtain an acceptable print quality in the case of a stationarily impressed, broad surface area character, it was learned that a relatively high pressure must be established between the electrode and the film in conjunction with a relatively high voltage applied thereto in order to commence arcing. it was also learned that the provision of a resilient pad supporting the film bearing substrate during arcing contributes substantiallyto print quality. It further became apparent that relative lateral movement during printing between the electrode and the film causes substantial broadening or smearing of the print.

Among the objectives of this invention is the provision of a system for arc printing characters upon a conductive film bearing substrate which creates prints of desirable quality.

SUMMARY OF THE INVENTION One aspect of the invention comprises a system for arc printing characters on a metallic film bearing substrate comprising a printing member having thereon at least one character shaped electrode, means for moving the printing member into contact with the film in a path of movement including a segment substantially perpendicular to the film upon contact therewith, and means for electrically connecting the electrode and the film to a power supply.

A further aspect of the invention comprises, in combination with a system for are printing characters on a metallic film bearing substrate, a printing member having thereon at least one character shaped electrode movable into contact with the film for arcing film off the substrate in the pattern of the electrode, means for separating the electrode and the film, and means operative when the electrode is separated from the film for removing metallic particles from the electrode.

Another feature comprises, in combination with a system for arc printing characters on a metallic film bearing substrate, a printing member having thereon at least one character shaped electrode for arcing film off the substrate in the pattern of the electrode, means for pressing the electrode against the film, and a resilient backing member for supporting the substrate in opposition to the pressing force. In those instances where the substrate is inherently resilient, the resilient character of the backing member may be omitted.

One specific embodiment of the invention includes a system for are printing characters on a metallic film bearing substrate comprising a printing member having thereon at least one character shaped electrode for areing film off the substrate in the pattern of the electrode, a non-conductive substrate having thereon an aluminum film of a thickness greater than at least approximately one hundred Angstroms, means for pressing the electrode against the film at a pressure of approximately pounds/square inch of character area, and means for electrically connecting the electrode and the film to a power supply delivering a potential in excess of at least approximately 16 volts.

In general, printing characteristics of metal coatings are influenced by the following factors:

1. The ability of the coating to conduct the required current to the impression to be printed. Low specific resistance and increasing thickness are beneficial in this respect.

2. Sufficient contact resistance to cause power dissipation at the print electrode. This power dissipation is that which destroys the coatings structural integrity in the impression and allows it to be removed. A thin natural oxide layer or a chemical surface treatment can produce the necessary contact resistance.

3. Decreasing thickness, density, specific heat, and melting point of the coating all tend to beneficially reduce the energy required to breakdown the coating during the printing process.

Experimental data relating some metal coatings to the above factors has shown that: aluminum is adequate in all three factors whereas copper and gold are deficient in (2) and (3); nickel and iron are deficient in (l), (2) and (3) while the properties of magnesium,

cadmium, indium, and zinc indicate that they might I provide adequate characteristics as indicated above,

although they have not been tested.

The parameters cited herein relate to the use of an aluminum coating since the same is highly satisfactory for the intended purpose. However, as would be suspected from the foregoing discussion a substitution of other type metal coatings would indicate that different parameters would be applicable. Thus, for example, where a coating thickness of 100 Angstroms is entirely suitable for aluminum, this value would be a function of the selected metallic coating having due regard to the general printing characteristics discussed above.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 illustrates, partly in isometric and partly in schematic, one embodiment of the invention; and

FIG. 2 is an enlarged view of the character shaped electrodes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is disclosed a printing system in accordance with this invention for are printing characters on a recordable medium 12 comprising a substrate 14 which is preferably transparent to allow optical projection of the characters printed on a conductive metallic film 16 bonded to the substrate 14. The system 10 comprises, as major components, a holder 18 for the medium 12, a printing member 20 having a plurality of character shaped electrodes 22 thereon, power means 24 for pressing the electrodes 22 against metallic film 16, an electricalsystem 26 for transmitting electrical current through the film l6 and electrodes 22 and a wiping mechanism 28 for removing metallic particles adhering to the electrodes 22.

The substrate 14 may be made from any of a rather large group of acceptable materials. If optical projection of the characters on the film 16 is not desired, the substrate may be of an opaque material such as the paper normally used in are printing media such as that found in the patents mentioned previously. If it is desired to optically project the characters on film l6, transparent or translucent organic polymers or glass operate quite satisfactorily. The substrate 14 is conveniently made of clear plastic sheeting of 0.002 0.01 inches in thickness which provides a flexible medium that is not subject to breaking.

The metallic film 16 may, likewise, be selected from a large group of acceptable materials such as those disclosed in the previously mentioned patents. A particularly convenient coating is aluminum evaporated onto the substrate 14. One of the difficulties encountered with the medium 12 is that the current capacity of commercially available material has been insufficient to handle the current necessary to are off the relatively large surface areas of the electrodes 22. Accordingly, the film 16 must have greater current carrying capacity and this is afforded by providing a thicker film coating than is used in stylus or trace recording. The film 16 is at least 100 Angstroms in thickness and the range of 100-300 Angstroms has proved satisfactory. One of the difficulties with an aluminum film is that it forms a surface layer of aluminum oxide which is, of course, an excellent insulator. In order to start the arcing between the relatively large area electrodes 22 and the film 16,

it has been found desirable to use relatively high voltage and to press the electrodes 22 firmly against the film 16 as will be more fully pointed out hereinafter.

The holder 18 may be of any suitable type and is illustrated as comprising a base 30 including an abutment 32 against which the medium 12 may be positioned. The holder 18 also comprises an insulating block 34 and an elongate electrical contact 36 secured to the abutment 32 in any convenient fashion. The electrical contact 36 also comprises part of the electrical system 26 and includes a plurality of metallic spring fingers 38 for engaging the film 16. The surface areas of the fingers 38 in contact with the film 16 preferably is substantially larger than the surfact area of the electrodes 22 to assure that the arcing takes place at the electrodes 22 rather than at the contact fingers 38.

An important feature of the holder 18 resides in the provision of a resilient pad 40 which supports the substrate 14 against a pressing force applied to the printing member 20. Since the electrodes 22 may have flat faces, as suggested by FIG. 2, it is highly desirable to provide a substantially uniform pressure between the electrodes 22 and the coating 16. Without the provision of the resilient pad 40, there is a tendency for film 16 to be removed in localized spots rather than completely along the area of the character shaped electrodes 22. With'the provision of the resilient pad 40, removal of the film 16 occurs substantially uniformly along the areas of the electrodes 22 and appears to be a result of the uniform pressure contact between the electrodes 22 and the film 16. The pad 40 may be made of any suitable resilient material, such as an elastomer greater than about .02 inches in thickness.

The printing member 20 comprises a base 42 made of insulating material such as insulation board to which the electrodes 22 are attached. As shown best in FIG. 2, the electrodes 22 are of character shape, such as numbers, letters or symbols, and present contact surfaces to the film 16 which are of relatively large surface area. The electrodes 22 may be captivated to the base 42 in any suitable fashion, as by providing a square shank 44 on the electrode 22 registering-with a square opening in the base 42. A suitable threaded fastener 46 may be used to retain the shank 44 in the opening. It will be readily apparent that an electrical connection through the base 42 can conveniently be made in conjunction with the fastener 46.

The pressing means 24 is illustrated in FIG. 1 as manipulating the printing member 20 although it will be appreciated that the medium 12 may, alternatively, be moved against the printing member 20. The pressing means 24 includes a first motor 48 which is illustrated as a pneumatic cylinder of any convenient construction. The cylinder 48 is equipped with suitable advance and retract air lines 50, 52 connected to a source of pressurized air 54 through suitable valving 56, 58. It will be apparent that the motor 48 may be powered in any desired fashion.

The valves 56, 58 are controlled through suitable electrical control lines 60, 62 connected to a control unit 64. The valves 56, 58 and the control unit 64 may be of any desired type. Conveniently, the valve 56 may be of the normally closed, self-venting type which may be opened to deliver pressurized fluid to the motor 48 and which, when closed, vents the air line 58 between the valve 56 and the motor 48. The valve 58 is conveniently of the normally open, self-venting type which when open delivers pressurized fluid to the motor 48 to retract the same and which, when closed, vents the air line 52 between the valve 58 and the motor 48. With this type valving, the motor 48 is normally retracted away from film 16.

The control unit 64 comprises a normally open switch 66 connecting the leads 60, 62 to a control power source 68. Closing of switch 66 causes valve 58 to close and vent and it also causes the valve 56 to open whereupon motor 48 advances printing member 20 toward film 16. Release of the switch 66 severs the electrical connection between the control power source 68 and valves 56, 58 whereupon the valve 56 closes and vents and the valve 58 opens to retract motor 48.

Delivery of air through the advance air line 50 causes motor 48 to extend thereby passing electrodes 22 on printing member 20 into contact with the film 16. As an assist in breaking down the aluminum oxide layer on film 16, the motor 48 preferably generates sufficient force so that the pressure on the contact surfaces of the electrodes 22 is at least 100 pounds/square inch. The character that is arced off the film 16 depends on which of the electrodes 22 is connected to the power source as will be apparent. It will be seen that printing member 20 is moved substantially perpendicularly into contact with the film l6. Lateral movement of theelectrodes 22 when in contact, or nearly in contact, with the film 16 is to be avoided since the characters arced therein become broader and are, in a sense, smeared.

The pressing means 24 also functions as a device to position the printing member 20 laterally with respect to the film 16 in order to print on a differentarea thereof. Accordingly, the motor!!! is illustrated as connected to a movable support 70 which is driven laterally with respect to the film 16 by asecond motor 72 which is controlled in any desired manner.

The electrical system 26 includes, as previously mentioned, the electrical contact 36 which is connected to a power supply 74 by a suitable lead 76. Connecting the power supply 74 to an electrode selector'switch 78 is a lead 80 having a suitable number of branches 82. The

switch 78 may comprise a suitable number of simple single pole, single'throw switch members 84 each of which is connected by a lead 86 to the exposed fastener 46 of each electrode 22.

The power supply 74 preferably delivers at least 16 volts potential across'contacts 22 and film 16 in order to assist breaking down the aluminum oxide surface layer of the film 16. Voltages in the range of 16-24 have proved quite satisfactory.

An important feature of the invention resides in the wiping mechanism 28. Experimentation with the printing system 10 revealed that the electrodes 22 accumulate metallic flakes or particles which have been arced off the film 16. After five to ten printing cycles have been made with a single electrode 22, degradation of the quality of the printed character thereof begins. The metallic flakes or particles appear to be either mechanically bonded or electrostatically attracted to the electrodes 22 and effectively change the contact surface of the electrodes 22 with the film 16 during succeeding printing operations. If the metallic particles are not periodically removed from the electrodes 22, the quality of the printed characters rapidly becomes unacceptable.

The wiping mechanism 28 comprises a wiping pad 88 made of felt, cloth or the like fixed to a base 90 which is mounted by a link 92 to a support 94 for movement into wiping engagement with the contact surfaces of the electrodes 22. The link 92 is connected to a motor 96 which may be of any convenient type but which is illustrated as a pneumatic motor having an advance air line 98 and a retract air line 100 connecting the motor 96 to a source of pressurized air 102. It will be apparent that wiping pad 88 is mounted for movement in a plane generally parallel to the bottom of electrodes 22 and that the electrodes 22 must be positioned at a predetermined height above the holder 18 in order for wiping contact to occur. The spacing of the electrodes 22 from the holder 18 is conveniently established by fully retracting the motor 48 and positioning the wiper pad 88 in the plane of the electrodes 22 in this position of the motor 48.

The electrodes 22 may be wiped after each printing cycle if desired. It presently appears, however, that wiping after five to ten printing cycles maintains print quality at a high level. Accordingly, cycling means are provided for cycling the motor 96 after a predetermined number of printing cycles. The cycling-means comprises-a normally closed self-venting valve'106 in the advance air line 98, a-normally open self-ventin'g valve 108 in the retract air line 100 and a counter 1 10 responsivetoa predetermined number of printing cycles for manipulating the valves 106, 108. The counter 110 is illustrated as electrically connected by a lead 112 to the'lead 62 for sensing the number of cycles of movementof the motor 48. The counter 1 10 senses the number of cycles of the motor 48 and activates the valves 106, 108 after a predetermined number of cycles througha pair of electrical leads 114, 116.- r

In use, the recordable medium 12 is placed on the resilient pad 40 so that the contact fingers 38 establish electrical contact with the film 16. The motor 72 is manipulat ed by suitable means (not shown) to position the desired electrode 22 adjacent the area to be printed. The switch 66 is then closed to advance the motor 48 and place the electrodes 22 in firm contact with the film 16.

The single pole, single throw switch 84 corresponding to the desired electrode to be printed is closed so that power is supplied to arc off the film l6 engaging the energized electrode 22. Release of switch 66 causes motor 48 to retract thereby separating the electrodes 22 from film 16 and exposing the printed character for viewing. The recordable medium 12 may be moved to a viewing position and, if the substrate 14 is transparent, optically projected.

After a predetermined number of printing cycles has occurred, the counter 1 10 triggers the valves 106, 108 to advance the motor 96 and thereby advance the pad 88 into wiping engagement withthe contacts 22. The bulk of the metallic particles adhering to the electrodes 22 are accordingly transferred to the pad 88. The counter 110 then manipulates the valves 186, 108 to retract the motor 96 and move the wiping pad 88 out of the path of movement of the printing member 20 in 0 preparation for the next printing cycle.

I claim: 1. A system for are printing characters on a metallic film bearing substrate comprising: a printing member having thereon a plurality of electrodes of different character shapes; means for moving the printing member into contact with the film in a path of movement including a segment substantially perpendicular to the film upon contact therewith, the moving means including means for moving the printing member laterally of the film while out of contact therewith; and

means for electrically connecting a selected electrode and the film to a power supply.

2. In combination with a system for are printing characters on a metallic film bearing substrate comprising:

a printing member having thereon at least one character shaped electrode for arcing film off the substrate in the pattern of the electrode;

means for pressing the electrode against the film; and

a resilient backing member for supporting the substrate in opposition to the pressing force.

3. The combination of claim 2 wherein the pressing .i' means includes means for pressing the electrode against the film at a pressure of at least approximately 100 pounds/square inch of character area.

4. The combination of claim 2 wherein the resilient backing member comprises an elastomer at least 0.02 inches in thickness.

5. The combination of claim 2 wherein the printing member provides thereon a plurality of electrodes of different character shapes.

6. A system for are printing characters on a metallic film bearing substrate comprising a printing member having thereon a plurality of electrodes of different character shapes; means mounting the printing member and the substrate for relative movement toward and away from each other and for movement laterally of each other; and means for electrically connecting a selected one of the electrodes and the film to a power supply. 7. A system for are printing characters on a metallic film bearing substrate comprising printing means comprising a plurality of electrodes of different character shape for arcing film off the substrate in the pattern of the electrodes; means for pressing at least one of the electrodes against the film; a resilient backing member for supporting the substrate in opposition to the pressing force; and means for electrically connecting the one electrode and the film to a power supply. 

1. A system for arc printing characters on a metallic film bearing substrate comprising: a printing member having thereon a plurality of electrodes of different character shapes; means for moving the printing member into contact with the film in a path of movement including a segment substantially perpendicular to the film upon contact therewith, the moving means including means for moving the printing member laterally of the film while out of contact therewith; and means for electrically connecting a selected electrode and the film to a power supply.
 2. In combination with a system for arc printing characters on a metallic film bearing substrate comprising: a printing member having thereon at least one character shaped electrode for arcing film off the substrate in the pattern of the electrode; means for pressing the electrode against the film; and a resilient backing member for supporting the substrate in opposition to the pressing force.
 3. The combination of claim 2 wherein the pressing means includes means for pressing the electrode against the film at a pressure of at least approximately 100 pounds/square inch of character area.
 4. The combination of claim 2 wherein the resilient backing member comprises an elastomer at least 0.02 inches in thickness.
 5. The combination of claim 2 wherein the printing member provides thereon a plurality of electrodes of different character shapes.
 6. A system for arc printing characters on a metallic film bearing substrate comprising a printing member having thereon a plurality of electrodes of different character shapes; means mounting the printing member and the substrate for relative movement toward and away from each other and for movement laterally of each other; and means for electrically connecting a selected one of the electrodes and the film to a power supply.
 7. A system for arc printing characters on a metallic film bearing substrate comprising printing means comprising a plurality of electrodes of different character shape for arcing film off the substrate in the pattern of the electrodes; means for pressing at least one of the electrodes against the film; a resilient backing member for supporting the substrate in opposition to the pressing force; and means for electrically connecting the one electrode and the film to a power supply. 